Control system, control method, control device, and program

ABSTRACT

A control system is a control system of casting and rolling equipment having a twin roll-type continuous casting machine, a rolling mill, and a conveyor. The control system includes a rolling mill control unit that controls the rolling mill by any one of controls including a rolling control and an open control, a conveyor control unit that controls the conveyor by any one of controls including a tension control and a speed control, a first control unit that controls to perform the rolling control and the tension control, a second control unit that controls to perform the open control and the speed control, and a third control unit that controls to resume the tension control and the rolling control.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a control system, a control method, acontrol device, and a program.

The present application claims priority based on Japanese PatentApplication No. 2018-205622 filed in Japan on Oct. 31, 2018, thecontents of which are incorporated herein by reference.

RELATED ART

A rolling mill having a rolling roll has been conventionally used toroll a material to be rolled such as a steel sheet. In this regard,Patent Document 1 discloses a technique of opening and closing a rollingroll by performing a first control and a second control. The firstcontrol is a control for opening the rolling roll. In the first control,the control is performed such that the rolling roll is in a non-contactstate with the material from a state of being closed to the material tobe rolled in a state where the material to be rolled in a rolled stateis decelerated from a speed at a time of rolling to an extremely lowspeed and tension of the material to be rolled on an inlet side and anexit side of the rolling mill is equal to each other. The second controlis a control for closing the rolling roll. In the second control, thecontrol is performed such that the rolling roll is closed from an openstate that is in non-contact with the material to be rolled and then isaccelerated to a speed during normal rolling in a state where the speedof the material to be rolled is in an extremely low speed, which islower than the speed during normal rolling, and in a state where anotherpredetermined condition is satisfied.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, FirstPublication No. 2014-58001

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

By the way, there is a case where the material to be rolled that isconveyed to the rolling mill has an abnormality such as a hot band ormeandering. The rolling may not be performed normally when the rollingis continued in a case where the material to be rolled that is conveyedto the rolling mill has the abnormality. Therefore, it is necessary toopen the rolling roll.

However, when the rolling roll is suddenly open in a state where atension control is performed in which predetermined tension is appliedto the material to be rolled, torque of a motor that rotates a pinchroll suddenly fluctuates. The material to be rolled slips against thepinch roll and the pinch roll defects. Therefore, unsteady work such asadjustment and replacement of the pinch roll is required, and a timeduring which the rolling cannot be performed increases. When the statewhere the material to be rolled continues to slip against the pinchroll, the predetermined tension cannot be applied to the material to berolled and a state where the material to be rolled cannot be rollednormally continues. Patent Document 1 does not describe the control in acase where there is the abnormality in the material to be rolled that isconveyed to the rolling mill.

An object of the present invention is to make it possible to continuethe rolling stably.

Means for Solving the Problem

The outline of the present invention is as follows.

(1) A first aspect of the present invention is a control system ofcasting and rolling equipment including a twin roll-type continuouscasting machine, a rolling mill that rolls a steel sheet with a pair ofrolling rolls, and a conveyor that conveys the steel sheet in adirection of the rolling mill with a pair of conveyance rolls, in whichthe twin roll-type continuous casting machine includes a pair of castingrolls that rotate in directions opposite to each other, the pair of thecasting rolls cools molten steel injected into an upper pouring basinbetween the pair of the casting rolls and pressure-contacts the cooledand solidified molten steel to discharge the steel sheet from betweenthe pair of the casting rolls, and the conveyor conveys the steel sheetdischarged from the twin roll-type continuous casting machine in thedirection of the rolling mill. The control system includes a rollingmill control unit that controls the rolling mill by any one of controlsincluding a rolling control of rolling the steel sheet with a set rollgap and an open control that performs a control such that at least oneof the pair of the rolling rolls does not contact the steel sheet, aconveyor control unit that controls the conveyor by any one of controlsincluding a tension control that conveys the steel sheet at set tensionof the steel sheet and a speed control that conveys the steel sheet at aset rotation speed of the conveyance rolls, a first control unit thatcontrols the rolling mill control unit to perform the rolling controland controls the conveyor control unit to perform the tension control, asecond control unit that controls the rolling mill control unit toperform the open control and controls the conveyor control unit toperform the speed control in a case where determination is made thatthere is an abnormality in the steel sheet while the rolling control andthe tension control started by the control by the first control unit areperformed, and a third control unit that controls the conveyor controlunit to resume the tension control and controls the rolling mill controlunit to resume the rolling control in a case where determination is madethat the conveyance rolls are stabilized at the set rotation speed bythe speed control started by the control by the second control unit.

(2) In the control system according to (1), the rolling mill controlunit may control the rolling mill by any one of controls including therolling control, the open control, and a light reduction control thatlightly reduces the steel sheet with a roll gap larger than the set rollgap. The third control unit may control the rolling mill control unit toperform the light reduction control, then control the conveyor controlunit to resume the tension control, and then control the rolling millcontrol unit to resume the rolling control, in a case wheredetermination is made that the pair of conveyance rolls are stabilizedat the set rotation speed by the speed control started by the control bythe second control unit.

(3) In the control system according to (2), the third control unit maycontrol the rolling mill control unit to perform the light reductioncontrol, then control the conveyor control unit to resume the tensioncontrol, and then control the rolling mill control unit to resume therolling control in a case where determination is made such that there isno abnormality in the steel sheet, in a case where determination is madethat the pair of conveyance rolls is stabilized at the set rotationspeed by the speed control started by the control of the second controlunit. The second control unit may control the rolling mill control unitto perform the open control and controls the conveyor control unit toperform the speed control, in a case where a determination is made thatthere is an abnormality in the steel sheet after the tension control isresumed by the control of the third control unit or in a case wheredetermination is made that there is an abnormality in the steel sheetwhile the rolling control and the tension control started by the controlof the first control unit are performed.

(4) In the control system according to (1), an abnormality determinationunit that determines that there is the abnormality in the steel sheet ina case where determination is made that the steel sheet meanders or acase where determination is made that there is an abnormal sheetthickness fluctuation in the steel sheet or a combination thereof isfurther included. The second control unit may control the rolling millcontrol unit to perform the open control and controls the conveyorcontrol unit to perform the speed control, in a case where theabnormality determination unit determines that there is the abnormalityin the steel sheet while the rolling control and the tension controlstarted by the control by the first control unit are performed.

(5) In the control system according to (4), the abnormalitydetermination unit may determine whether or not the abnormal sheetthickness fluctuation occurs in the steel sheet based on a current of amotor that rotates the rolling roll.

(6) In the control system according to (1), a speed determination unitthat determines that the conveyance rolls are stabilized at the setrotation speed in a case where the rotation speed of the conveyancerolls continuously falls in a set range for a set time is furtherincluded. The third control unit may control the conveyor control unitto resume the tension control and controls the rolling mill control unitto resume the rolling control, in a case where the speed determinationunit determines that the conveyance rolls are stabilized at the setrotation speed after the speed control is started by the control by thesecond control unit.

(7) A second aspect of the present invention is a control method ofcasting and rolling equipment including a twin roll-type continuouscasting machine, a rolling mill that rolls a steel sheet with a pair ofrolling rolls, a conveyor that conveys the steel sheet in a direction ofthe rolling mill with a pair of conveyance rolls, a rolling mill controlunit that controls the rolling mill by any one of controls including arolling control of rolling the steel sheet with a set roll gap and anopen control that performs a control such that at least one of the pairof the rolling rolls does not contact the steel sheet, a conveyorcontrol unit that controls the conveyor by any one of controls includinga tension control that conveys the steel sheet at set tension of thesteel sheet and a speed control that conveys the steel sheet at a setrotation speed of the conveyance rolls, in which the twin roll-typecontinuous casting machine includes a pair of casting rolls that rotatesin directions opposite to each other, the pair of the casting rollscools molten steel injected into an upper pouring basin between the pairof the casting rolls and pressure-contacts the cooled and solidifiedmolten steel to discharge the steel sheet from between the pair of thecasting rolls, and the conveyor conveys the steel sheet discharged fromthe twin roll-type continuous casting machine in the direction of therolling mill. The control method includes a first control step ofcontrolling the rolling mill control unit to perform the rolling controland controlling the conveyor control unit to perform the tensioncontrol, a second control step of controlling the rolling mill controlunit to perform the open control and controlling the conveyor controlunit to perform the speed control in a case where determination is madethat there is an abnormality in the steel sheet while the rollingcontrol and the tension control started by the control by the firstcontrol step are performed, and a third control step of controlling theconveyor control unit to resume the tension control and controlling therolling mill control unit to resume the rolling control, in a case wheredetermination is made that the conveyance rolls are stabilized at theset rotation speed by the speed control started by the control by thesecond control step.

(8) A third aspect of the present invention is a control device thatcontrols casting and rolling equipment including a twin roll-typecontinuous casting machine, a rolling mill that rolls a steel sheet witha pair of rolling rolls, a conveyor that conveys the steel sheet in adirection of the rolling mill with a pair of conveyance rolls, a rollingmill control unit that controls the rolling mill by any one of controlsincluding a rolling control of rolling the steel sheet with a set rollgap and an open control that performs a control such that at least oneof the pair of the rolling rolls does not contact the steel sheet, aconveyor control unit that controls the conveyor by any one of controlsincluding a tension control that conveys the steel sheet at set tensionof the steel sheet and a speed control that conveys the steel sheet at aset rotation speed of the conveyance rolls, in which the twin roll-typecontinuous casting machine includes a pair of casting rolls that rotatesin directions opposite to each other, the pair of the casting rollscools molten steel injected into an upper pouring basin between the pairof the casting rolls and pressure-contacts the cooled and solidifiedmolten steel to discharge the steel sheet from between the pair of thecasting rolls, and the conveyor conveys the steel sheet discharged fromthe twin roll-type continuous casting machine in the direction of therolling mill. The control device includes a first control unit thatcontrols the rolling mill control unit to perform the rolling controland controls the conveyor control unit to perform the tension control, asecond control unit that controls the rolling mill control unit toperform the open control and controls the conveyor control unit toperform the speed control in a case where determination is made thatthere is an abnormality in the steel sheet while the rolling control andthe tension control started by the control by the first control unit areperformed, and a third control unit that controls the conveyor controlunit to resume the tension control and controls the rolling mill controlunit to resume the rolling control in a case where determination is madethat the conveyance rolls are stabilized at the set rotation speed bythe speed control started by the control by the second control unit.

(9) A fourth aspect of the present invention is a program that controlscasting and rolling equipment including a twin roll-type continuouscasting machine, a rolling mill that rolls a steel sheet with a pair ofrolling rolls, a conveyor that conveys the steel sheet in a direction ofthe rolling mill with a pair of conveyance rolls, a rolling mill controlunit that controls the rolling mill by any one of controls including arolling control of rolling the steel sheet with a set roll gap and anopen control that performs a control such that at least one of the pairof the rolling rolls does not contact the steel sheet, a conveyorcontrol unit that controls the conveyor by any one of controls includinga tension control that conveys the steel sheet at set tension of thesteel sheet and a speed control that conveys the steel sheet at a setrotation speed of the conveyance rolls, in which the twin roll-typecontinuous casting machine includes a pair of casting rolls that rotatesin directions opposite to each other, the pair of the casting rollscools molten steel injected into an upper pouring basin between the pairof the casting rolls and pressure-contacts the cooled and solidifiedmolten steel to discharge the steel sheet from between the pair of thecasting rolls, and the conveyor conveys the steel sheet discharged fromthe twin roll-type continuous casting machine in the direction of therolling mill. The program causing a computer to function as a firstcontrol unit that controls the rolling mill control unit to perform therolling control and controls the conveyor control unit to perform thetension control, a second control unit that controls the rolling millcontrol unit to perform the open control and controls the conveyorcontrol unit to perform the speed control in a case where determinationis made that there is an abnormality in the steel sheet while therolling control and the tension control started by the control by thefirst control unit are performed, and a third control unit that controlsthe conveyor control unit to resume the tension control and controls therolling mill control unit to resume the rolling control in a case wheredetermination is made that the conveyance rolls are stabilized at theset rotation speed by the speed control started by the control by thesecond control unit.

EFFECTS OF THE INVENTION

According to the present invention, it is possible to continue therolling stably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of a configuration of a castingand rolling system.

FIG. 2A is a diagram showing an example of a hardware configuration of amain control device.

FIG. 2B is a diagram showing an example of a hardware configuration of aconveyor control device.

FIG. 3 is a diagram showing an example of a functional configuration ofthe main control device.

FIG. 4A is a diagram for describing a tension control.

FIG. 4B is a diagram for describing a speed control.

FIG. 5A is a perspective view of an example of a casting portion of atwin roll-type continuous casting machine.

FIG. 5B is a plan view of an example of the casting portion.

FIG. 5C is a perspective view of an example of a steel sheet on which ahot band is formed.

FIG. 6 is a diagram showing a rolling motor current graph and the like.

FIG. 7 is a cross-sectional view of an example of the steel sheet.

FIG. 8A is a diagram showing a casting roll speed graph.

FIG. 8B is a diagram showing a first pinch roll speed graph.

FIG. 8C is a diagram showing a second pinch roll speed graph.

FIG. 8D is a diagram showing a rolling roll speed graph.

FIG. 9 is a flowchart showing an example of control processing.

FIG. 10A is a diagram showing the casting roll speed graph.

FIG. 10B is a diagram showing the first pinch roll speed graph.

FIG. 10C is a diagram showing the second pinch roll speed graph.

FIG. 10D is a diagram showing the rolling roll speed graph.

EMBODIMENTS OF THE INVENTION Overall Configuration

First, a casting and rolling system 1 according to the presentembodiment will be described with reference to FIG. 1 . FIG. 1 is adiagram showing an example of a configuration of the casting and rollingsystem 1. The casting and rolling system 1 has casting and rollingequipment 100 and a control system 101, and casts and rolls a steelsheet 10 as a material to be rolled. In this embodiment, the bottom is adirection of gravity and the top is an opposite direction of gravity.

The casting and rolling equipment 100 includes a twin roll-typecontinuous casting machine 150, a processing chamber 250, coolingequipment 252, a meandering meter 254, a conveyor 300, a rolling mill350, a looper 400, and a coiler 450.

The twin roll-type continuous casting machine 150 is a casting machinethat manufactures the steel sheet 10 from molten steel and includes aninjection portion 160 and a casting portion 200.

The injection portion 160 is a device for injecting the molten steelinto the casting portion 200 and includes a tundish 161 and a stopper162.

The tundish 161 is a container that temporarily receives the moltensteel injected from a ladle. The molten steel injected into the tundish161 is injected into a pouring basin 210 of the casting portion 200through a spout which is a through-hole provided in the lower part ofthe tundish 161.

The stopper 162 is a rod-shaped member that can open and close the spoutprovided in the lower part of the tundish 161, is disposed above thespout, and elongates in the vertical direction. The stopper 162 moves inthe vertical direction and thus an amount of the molten steel injectedfrom the tundish 161 into the casting portion 200 changes. When thestopper 162 moves to the lowermost position to close the spout of thetundish 161, the molten steel is not injected from the tundish 161 intothe casting portion 200.

The casting portion 200 manufactures the steel sheet 10 from the moltensteel injected from the injection portion 160. The casting portion 200includes a pair of casting rolls 201, a pair of weirs 202, a castingmotor 205, and a casting machine speedometer 206.

Each of the casting rolls of the pair of casting rolls 201 is a columnarroll and is rotatable around a central axis as a rotation axis. The pairof casting rolls 201 has the same shape as each other, and therespective rotation axes are disposed to be substantially parallel onthe same horizontal plane. A gap referred to as a casting roll gap isprovided between the pair of casting rolls 201. Each of the castingrolls of the pair of casting rolls 201 rotate in directions opposite toeach other such that end portions on the casting roll gap side advancedownward. A region surrounded by an upper side of the casting roll gapand the weir 202 is the pouring basin 210 in which the molten steelinjected from the injection portion 160 is collected.

When each of the casting rolls of the pair of casting rolls 201 rotatesin a state where the molten steel is injected into the pouring basin210, the casting rolls 201 cool and solidify the molten steel on asurface of the casting roll 201. The pair of casting rolls 201pressure-contacts a solidified shell, which is solidified molten steel,to discharge the steel sheet 10 downward from the casting roll gap.

Each of the weirs of the pair of weirs 202 is provided at both ends ofthe casting roll 201 in a rotation axis direction and at least above thecasting roll gap to prevent the molten steel from spilling from thepouring basin 210 in the rotation axis direction of the casting roll201.

The casting motor 205 rotates each of the casting rolls of the pair ofcasting rolls 201.

The casting machine speedometer 206 measures a rotation speed of thecasting motor 205. The rotation speed of the casting motor 205corresponds to a casting roll speed. The casting roll speed is a speedof the surface of the casting roll 201 and is proportional to therotation speed of the casting motor 205. The casting roll speedrepresents a rotation speed of the casting roll 201.

The processing chamber 250 is filled with gas to prevent oxidation ofthe steel sheet 10 discharged from the twin roll-type continuous castingmachine 150.

The cooling equipment 252 is disposed between a first conveyor 300A anda second conveyor 300B and cools the steel sheet 10 by spraying coolingwater on the steel sheet 10 to be conveyed.

The meandering meter 254 measures an amount of meandering of the steelsheet 10 and outputs the measured amount to a main control device 500.The amount of meandering is an amount representing a difference betweena planned normal position of the steel sheet 10 in a directionperpendicular to a conveyance direction of the steel sheet 10 and anactual position of the steel sheet 10 in the direction perpendicular tothe conveyance direction of the steel sheet 10 in a case where the steelsheet 10 is viewed from above. The planned normal position is assumed tobe set in advance. In this embodiment, the meandering meter 254 isdisposed in front of the rolling mill 350. More specifically, themeandering meter 254 is disposed between the second conveyor 300B andthe rolling mill 350. However, the meandering meter 254 may be disposedbehind the rolling mill 350. More specifically, the meandering meter 254may be disposed between the rolling mill 350 and the looper 400.

The conveyor 300 pulls in the steel sheet 10 and discharges the steelsheet 10 in the conveyance direction to convey the steel sheet 10. Theconveyor 300 includes a pair of pinch rolls 301, a conveyance motor 303,and a conveyor speedometer 304.

Each of the pinch rolls of the pair of pinch rolls 301 is a columnarroll, is rotatable around a central axis as a rotation axis, and isdisposed to be side by side vertically. A gap referred to as a pinchroll gap is provided between the pair of pinch rolls 301. The pair ofpinch rolls 301 sandwiches the steel sheet 10 by passing the steel sheet10 through the pinch roll gap and rotates in directions opposite to eachother while pressurizing a surface of the steel sheet 10 to convey thesteel sheet 10. The pinch roll 301 is also referred to as a conveyanceroll.

The conveyance motor 303 rotates each of the pinch rolls of the pair ofpinch rolls 301. Torque of the conveyance motor 303 is proportional to acurrent flowing through the conveyance motor 303.

The conveyor speedometer 304 measures a rotation speed of the conveyancemotor 303. The rotation speed of the conveyance motor 303 corresponds toa pinch roll speed. The pinch roll speed is a speed of a surface of thepinch roll 301 and is proportional to the rotation speed of theconveyance motor 303. The pinch roll speed represents a rotation speedof the pinch roll 301.

The casting and rolling equipment 100 includes the first conveyor 300Aand the second conveyor 300B as the conveyor 300.

The first conveyor 300A is disposed at a position deviated from thecasting roll gap of the twin roll-type continuous casting machine 150when viewed from above. The first conveyor 300A pulls in the steel sheet10 discharged from the twin roll-type continuous casting machine 150 anddischarges the steel sheet 10 in a direction of the second conveyor 300Bto convey the steel sheet 10. The second conveyor 300B pulls in thesteel sheet 10 conveyed from the first conveyor 300A and discharges thesteel sheet 10 in a direction of the rolling mill 350 to convey thesteel sheet 10 to the rolling mill 350.

The pinch roll 301, the conveyance motor 303, the conveyor speedometer304, and the pinch roll speed of the first conveyor 300A arerespectively referred to as a first pinch roll 301A, a first conveyancemotor 303A, a first conveyor speedometer 304A, and a first pinch rollspeed.

The pinch roll 301, the conveyance motor 303, the conveyor speedometer304, and the pinch roll speed of the second conveyor 300B arerespectively referred to as a second pinch roll 301B, a secondconveyance motor 303B, a second conveyor speedometer 304B, and a secondpinch roll speed.

The rolling mill 350 rolls the steel sheet 10 conveyed from the secondconveyor 300B. The rolling mill 350 rolls the steel sheet 10 whilepulling in the steel sheet 10 and discharges the steel sheet 10 in theconveyance direction. The rolling mill 350 includes a pair of rollingrolls 351, a pair of backup rolls 352, a rolling mill power cylinder353, a rolling motor 354, and a rolling mill speedometer 355.

Each of the rolling rolls of the pair of rolling rolls 351 is a columnarroll, is rotatable around a central axis as a rotation axis, and isdisposed vertically side by side such that the respective rotation axesare parallel to each other. A gap referred to as a rolling roll gap isprovided between the pair of rolling rolls 351. The pair of rollingrolls 351 sandwiches the steel sheet 10 by passing the steel sheet 10through the rolling roll gap and rotates in directions opposite to eachother while adding force to pressurize the steel sheet 10 to roll thesteel sheet 10.

Each of the backup rolls of the pair of backup rolls 352 is a columnarroll, is rotatable about a central axis as a rotation axis, and isdisposed to be side by side vertically with the pair of rolling rolls351 sandwiched therebetween. An upper backup roll 352 is disposed abovean upper rolling roll 351 to be in contact with the upper rolling roll351. A lower backup roll 352 is disposed below a lower rolling roll 351to be in contact with the lower rolling roll 351.

The rolling mill power cylinder 353 is, for example, a hydraulic servocylinder and adds the force to the upper backup roll 352 to change therolling mill pressing force or the rolling roll gap. The conveyor powercylinder 302 applies the rolling mill pressing force to the steel sheet10 through the upper rolling roll 351. The rolling mill pressing forceis force that the rolling roll 351 pressurizes the steel sheet 10 toroll the steel sheet 10.

The rolling motor 354 rotates the pair of rolling rolls 351.

The rolling mill speedometer 355 measures a rotation speed of therolling motor 354. The rotation speed of the rolling motor 354corresponds to a rolling roll speed. The rolling roll speed is a speedof a surface of the rolling roll 351 and is proportional to the rotationspeed of the rolling motor 354. The rolling roll speed represents arotation speed of the rolling roll 351.

The looper 400 applies tension to the steel sheet 10. The looper 400according to the present embodiment is a counter balance weight typelooper. The looper 400 is disposed between the rolling mill 350 and thecoiler 450.

The coiler 450 pulls in the steel sheet 10 and winds up the steel sheet10.

The control system 101 controls the casting and rolling equipment 100.The control system 101 includes a main control device 500, a conveyorcontrol device 550, a rolling speed control device 570, and a rollinggap control device 580.

The main control device 500 is an information processing device thatcontrols the conveyor control device 550, the rolling speed controldevice 570, and the rolling gap control device 580 to control thecasting and rolling equipment 100.

The conveyor control device 550 is an information processing device thatcontrols the conveyor 300 based on the control of the main controldevice 500 to control the pinch roll 301. More specifically, theconveyor control device 550 controls the current of the conveyance motor303 included in the conveyor 300 to control the pinch roll 301. Thecontrol system 101 includes a first conveyor control device 550A and asecond conveyor control device 550B as the conveyor control device 550.The first conveyor control device 550A controls the first conveyor 300A.More specifically, the first conveyor control device 550A adjusts acurrent of the first conveyance motor 303A to control the first pinchroll 301A. The second conveyor control device 550B controls the secondconveyor 300B. More specifically, the second conveyor control device550B adjusts a current of the second conveyance motor 303B to controlthe second pinch roll 301B. For example, an inverter is used as theconveyor control device 550.

The rolling speed control device 570 is an information processing devicethat controls the rolling mill 350 based on the control of the maincontrol device 500 to control the rolling roll speed. More specifically,the rolling speed control device 570 controls a current of the rollingmotor 354 included in the rolling mill 350 to control the rolling rollspeed. For example, an inverter is used as the rolling speed controldevice 570.

The rolling gap control device 580 is an information processing devicethat controls the rolling mill 350 based on the control of the maincontrol device 500 to control the rolling roll gap. More specifically,the rolling gap control device 580 controls the rolling mill powercylinder 353 included in the rolling mill 350 to control the rollingroll gap. The rolling gap control device 580 is also referred to as arolling mill control device.

Next, a conveyance path of the steel sheet 10 in the casting and rollingequipment 100 will be described. First, the steel sheet 10 is dischargedfrom between the pair of casting rolls 201 of the twin roll-typecontinuous casting machine 150. Next, the steel sheet 10 passes betweenthe pair of first pinch rolls 301A included in the first conveyor 300Aand between the pair of second pinch rolls 301B included in the secondconveyor 300B. The steel sheet 10 is rolled between the pair of rollingrolls 351 of the rolling mill 350 and discharged to the looper 400.Next, the steel sheet 10 passes through the looper 400 and is wound bythe coiler 450.

Hardware Configuration

Next, a hardware configuration of the main control device 500 will bedescribed with reference to FIG. 2A. FIG. 2A is a diagram showing anexample of the hardware configuration of the main control device 500.

The main control device 500 is a computer such as a programmable logiccontroller (PLC) and includes a CPU 501, a storage device 502, acommunication interface 503, an input device 504, and a bus 505connecting them.

The CPU 501 controls the entire main control device 500. The CPU 501executes processing based on a program stored in the storage device 502or the like to realize a function of the main control device 500 shownin FIG. 3 or processing of FIG. 9 .

The storage device 502 is a storage medium such as a RAM, a ROM, or anHDD, and stores the program or temporarily stores data used by the CPU501.

The communication interface 503 controls communication between the maincontrol device 500 and the conveyor control device 550, the rollingspeed control device 570, or the rolling gap control device 580.

The input device 504 receives an input from an operator. Variousswitches or buttons, a touch panel, a keyboard, a mouse, or the like areused as the input device 504.

The main control device 500 has a function of virtually dividing the CPU501 and can perform parallel processing. The CPU 501 can acquireinformation of a measuring instrument of the casting and rollingequipment 100 through the communication interface 503. The measuringinstrument of the casting and rolling equipment 100 is a device foracquiring various pieces of information of the casting and rollingequipment 100 and includes the meandering meter 254 and the speedometersuch as the casting machine speedometer 206 or the rolling millspeedometer 355.

Next, a hardware configuration of the conveyor control device 550 willbe described with reference to FIG. 2B. FIG. 2B is a diagram showing anexample of the hardware configuration of the conveyor control device550.

The conveyor control device 550 is a computer such as an inverter andincludes a CPU 551, a storage device 552, a communication interface 553,and a bus 554 connecting them.

The CPU 551 controls the entire conveyor control device 550. The CPU 551executes processing based on a program stored in the storage device 552or the like to realize a function of the conveyor control device 550shown in FIG. 4A or FIG. 4B.

The storage device 552 is a storage medium such as a RAM, a ROM, or anHDD, and stores the program or temporarily stores data used by the CPU551.

The communication interface 553 controls communication between theconveyor control device 550 and the main control device 500 or theconveyor 300.

Hardware configurations of the rolling speed control device 570 and therolling gap control device 580 are the same as that of the conveyorcontrol device 550. For example, a CPU of the rolling gap control device580 executes processing based on a program stored in a storage device orthe like of the rolling gap control device 580 to realize a function ofthe rolling gap control device or the like.

Functional Configuration

Next, a functional configuration of the main control device 500 will bedescribed with reference to FIG. 3 . FIG. 3 is a diagram showing anexample of the functional configuration of the main control device 500.The main control device 500 includes a first control unit 510, a secondcontrol unit 511, a third control unit 512, an abnormality determinationunit 514, a speed determination unit 515, a tension determination unit516, and a processing management unit 517.

The first control unit 510 controls the rolling gap control device 580to perform a rolling control and controls the conveyor control device550 to perform a tension control. The rolling control and the tensioncontrol will be described below.

The second control unit 511 controls the rolling gap control device 580to perform an open control and controls the conveyor control device 550to perform a speed control in a case where determination is made thatthere is an abnormality in the steel sheet 10 when the rolling controland the tension control started by the control by the first control unit510 are performed. The open control and the speed control will bedescribed below.

The third control unit 512 controls the conveyor control device 550 toresume the tension control and controls the rolling gap control device580 to resume the rolling control in a case where determination is madethat the first pinch roll speed is stabilized at a first speed and thesecond pinch roll speed is stabilized at a second speed by the speedcontrol started by the control by the second control unit 511.

The first speed and the second speed are speeds set in advance accordingto characteristics of the casting and rolling equipment 100 or the like.The first speed and the second speed may be the same speed. The firstspeed and the second speed are, for example, the casting roll speeds atthe time of casting and rolling in the casting and rolling equipment100.

The abnormality determination unit 514 determines that there is theabnormality in the steel sheet 10 in a case where determination is madethat the steel sheet 10 meanders or a case where determination is madethat there is an abnormal sheet thickness fluctuation in the steel sheet10 or a combination thereof. An example of the abnormal sheet thicknessfluctuation in the steel sheet 10 is a hot band described below.

The speed determination unit 515 determines that the first pinch rollspeed is stabilized at the first speed in a case where the first pinchroll speed continuously falls in a first speed range during a firstspeed determination time. The speed determination unit 515 determinesthat the second pinch roll speed is stabilized at the second speed in acase where the second pinch roll speed continuously falls in a secondspeed range during a second speed determination time.

The first speed range is a range of speed including the first speed. Thesecond speed range is a range of speed including the second speed.Appropriate values of the first speed range, the second speed range, thefirst speed determination time, and the second speed determination timefor the casting and rolling equipment 100 are determined by asimulation, an experiment, or the like.

The tension determination unit 516 determines that rear surface tensionof the first conveyor 300A is stabilized at first tension in a casewhere the rear surface tension of the first conveyor 300A continuouslyfalls in a first tension range during a first tension determinationtime. The tension determination unit 516 determines that rear surfacetension of the second conveyor 300B is stabilized at second tension in acase where the rear surface tension of the second conveyor 300Bcontinuously falls in a second tension range during a second tensiondetermination time.

The first tension and the second tension are set in advance according toa type of the steel sheet 10, an amount of rolling, or the like. Thefirst tension range is a range of tension including the first tension.The second tension range is a range of tension including the secondtension. Appropriate values of the first tension range, the secondtension range, the first tension determination time, and the secondtension determination time for the casting and rolling equipment 100 aredetermined by a simulation, an experiment, or the like.

Rear surface tension of the conveyor 300 is tension of the steel sheet10 on a rear side of the conveyor 300 (advancing direction side of thesteel sheet 10). For example, the rear surface tension of the firstconveyor 300A is tension between the first pinch roll 301A and thesecond pinch roll 301B, which is a roll on a rear side of the firstpinch roll 301A. The rear surface tension of the second conveyor 300B istension between the second pinch roll 301B and the rolling roll 351which is a roll on a rear side of the second pinch roll 301B. The rearsurface tension of the conveyor 300 is also referred to as rear surfacetension of the pinch roll 301. The rear surface tension of the firstconveyor 300A and the rear surface tension of the second conveyor 300Bare also respectively referred to as rear surface tension of the firstpinch roll 301A and rear surface tension of the second pinch roll 301B.

The processing management unit 517 controls each function included inthe main control device 500 or the like.

Next, the functional configuration of the conveyor control device 550will be described. The conveyor control device 550 has a conveyorcontrol unit. The conveyor control unit controls the conveyor 300 by anyone of the controls including the tension control and the speed control.The conveyor control unit includes a tension control unit 560 thatperforms the tension control and a speed control unit 561 that performsthe speed control. The conveyor control unit may be configured such thatthe conveyor 300 can be controlled by a control other than the tensioncontrol and the speed control.

First, the tension control performed by the tension control unit 560will be described with reference to FIG. 4A. FIG. 4A is a diagram fordescribing the tension control.

The tension control is a control for the tension control unit 560 toconvey the steel sheet 10 with the rear surface tension of the pinchroll 301 as setting tension which is set tension. The tension controlunit 560 of the conveyor control device 550 performs the tensioncontrol, so that the conveyor 300 conveys the steel sheet 10 with therear surface tension of the pinch roll 301 as the setting tension. Thetension control unit 560 of the first conveyor control device 550A usesthe first tension already described as the setting tension. The tensioncontrol unit 560 of the second conveyor control device 550B uses thesecond tension already described as the setting tension.

The tension control performed by the tension control unit 560 will bedescribed in more detail.

As first processing, the tension control unit 560 determines a torquelimit based on the setting tension. The torque limit is an upper limitof the torque of the conveyance motor 303 controlled by the tensioncontrol unit 560. The tension control unit 560 controls the torque ofthe conveyance motor 303 so as not to exceed the determined torquelimit.

Next, as second processing, the tension control unit 560 controls theconveyance motor 303 such that the pinch roll speed of the pinch roll301 corresponding to the conveyance motor 303 controlled by the tensioncontrol unit 560 is slower than a roll speed of the roll adjacent to therear side by a differential speed command. The tension control unit 560is assumed to acquire the differential speed command in advance from themain control device 500.

With the second processing, the pinch roll speed of the pinch roll 301corresponding to the conveyance motor 303 controlled by the tensioncontrol unit 560 becomes slower than the roll speed of the roll adjacentto the rear side by the differential speed command Therefore, the torqueof the conveyance motor 303 controlled by the tension control unit 560gradually increases, and finally the torque of the conveyance motor 303becomes constant at the torque limit determined in the first processing.This torque limit corresponds to the setting tension. Therefore, whenthe torque of the conveyance motor 303 reaches the torque limit, thetension of the steel sheet 10 is stabilized at the setting tension.However, the tension control unit 560 may perform the tension control bya method other than the tension control described here.

Next, the speed control performed by the speed control unit 561 will bedescribed with reference to FIG. 4B. FIG. 4B is a diagram for describingthe speed control.

The speed control is a control for the conveyor 300 to convey the steelsheet 10 with the pinch roll speed as a setting speed which is a setspeed. The speed control unit 561 of the conveyor control device 550controls the speed, so that the conveyor 300 conveys the steel sheet 10with the pinch roll speed as the setting speed. The speed control unit561 of the first conveyor control device 550A uses the first speedalready described as the setting speed. The speed control unit 561 ofthe second conveyor control device 550B uses the second speed alreadydescribed as the setting speed.

The speed control performed by the speed control unit 561 will bedescribed in more detail.

The speed control unit 561 calculates an actual value of the pinch rollspeed based on the rotation speed of the conveyance motor 303 acquiredfrom the conveyor speedometer 304.

Next, the speed control unit 561 determines the current flowing throughthe conveyance motor 303 such that the pinch roll speed approaches thesetting speed, based on a difference between the actual value of thepinch roll speed and the setting speed.

Next, the speed control unit 561 controls such that the determinedcurrent flows through the conveyance motor 303.

By repeating the processing, the speed control unit 561 controls theconveyor 300 to convey the steel sheet 10 with the pinch roll speed asthe setting speed.

Next, a functional configuration of the rolling speed control device 570will be described. The rolling speed control device 570 includes a speedcontrol unit. The speed control unit of the rolling speed control device570 controls the rolling motor 354 such that the rolling mill 350conveys the steel sheet 10 with the rolling roll speed as a set rollingroll speed, using the same control method as the speed control unit 561of the conveyor control device 550.

Next, a functional configuration of the rolling gap control device 580will be described. The rolling gap control device 580 has a rolling millcontrol unit. The rolling mill control unit controls the rolling mill350 by any one of controls including the rolling control, the opencontrol, and a light reduction control. The rolling mill control unitincludes a rolling control unit that performs the rolling control, anopen control unit that performs the open control, and a light reductioncontrol unit that performs a light reduction control. The rolling millcontrol unit may be configured such that the rolling mill 350 can becontrolled by a control other than the rolling control, the opencontrol, and the light reduction control.

The rolling control unit performs the rolling control that controls therolling mill power cylinder 353 of the rolling mill 350 to roll thesteel sheet 10 with the rolling roll gap as a first rolling roll gap.When the rolling control is performed, the tension control is performedby the tension control unit 560 in the conveyor control device 550. Thisis to stably perform the rolling by applying the set tension to thesteel sheet 10 when the steel sheet 10 is rolled by the rolling control,for example. The first rolling roll gap is set in advance as a rollingparameter.

The open control unit performs the open control that controls therolling mill power cylinder 353 such that at least one of the pair ofrolling rolls 351 does not contact the steel sheet 10. The state whereat least one of the pair of rolling rolls 351 does not contact the steelsheet 10 is referred to as roll opening.

The light reduction control unit performs the light reduction controlthat controls the rolling mill power cylinder 353 of the rolling mill350 such that the steel sheet 10 is lightly reduced with the rollingroll gap as a second rolling roll gap. The second rolling roll gap is avalue larger than the first rolling roll gap.

Hot Band

Next, a hot band 13 of the steel sheet 10, which is an example of theabnormal sheet thickness fluctuation of the steel sheet 10, will bedescribed with reference to FIGS. 5A, 5B, and 5C. FIG. 5A is aperspective view of an example of the casting portion 200 of the twinroll-type continuous casting machine 150. FIG. 5B is a plan view of anexample of the casting portion 200. FIG. 5C is a perspective view of anexample of the steel sheet 10 on which the hot band 13 is formed.

As shown in FIG. 5C, the hot band 13 is a thick portion of the steelsheet 10 formed by a base metal 12 on a side surface of the weir 202entering during the casting. The base metal 12 on the side surface ofthe weir 202 as shown in FIG. 5A is formed by solidifying molten steel11 adhering to the side surface of the weir 202 due to a fluctuation ina molten metal surface level (surface height of the molten steel 11)during the casting or the like.

The base metal 12 on the side surface of the weir 202 may be peeled offfrom the weir 202 due to an end portion on a lower side of the basemetal 12 being caught in the casting roll 201 or the like, and may enterbetween the pair of casting rolls 201 as shown in FIG. 5B. When the basemetal 12 enters between the pair of casting rolls 201, a space betweenthe pair of casting rolls 201 is widened due to hardness of the basemetal 12, and the steel sheet 10 on which the hot band 13 is formed isdischarged from the twin roll-type continuous casting machine 150 asshown in FIG. 5C.

For example, in a normal continuous casting machine having a tundish, amold, and a plurality of rolls and in which molten steel discharged fromthe tundish is cooled through the mold and conveyed to the plurality ofrolls to manufacture a steel sheet, a powder having a function as a heatinsulating material is put into the mold. This powder flows between themold and a solidified shell and also acts as a lubricant. Therefore, anamount of base metal adhering to a side surface of the mold due to thefluctuation in the molten metal surface level is small. On the otherhand, in the twin roll-type continuous casting machine, rapid cooling isgenerally required. Therefore, the powder having the function as theheat insulating material and the lubricant is not input. Therefore, thelubricity is inferior to that of a normal continuous casting machine.Therefore, in the twin roll-type continuous casting machine, an amountof adhesion of the base metal 12 on the side surface of the weir 202 islarger than the amount of adhesion of the base metal on the side surfaceof the mold in the normal continuous casting machine. Therefore, in thecase of the twin roll-type continuous casting machine, the hot band 13is generally likely to be formed.

Detection Method of Hot Band Occurrence

Next, a detection method of hot band occurrence will be described withreference to FIG. 6 . FIG. 6 is a diagram showing a rolling motorcurrent graph 600 and a rolling roll speed graph 601.

The rolling motor current graph 600 of FIG. 6 shows a time change of thecurrent flowing through the rolling motor 354 when the casting androlling system 1 actually performs the casting and the rolling. Therolling roll speed graph 601 of FIG. 6 shows a time change of therolling roll speed when the casting and rolling system 1 actuallyperforms the casting and the rolling. In the rolling roll speed graph601, the rolling roll speed is represented in units of mpm(meters/minute). When data of FIG. 6 is acquired, the rolling speedcontrol device 570 controls the speed control unit to perform the speedcontrol and the rolling gap control device 580 controls the rollingcontrol unit to perform the rolling control. In the rolling motorcurrent graph 600, the hot band 13 of the steel sheet 10 reaches therolling roll 351 at a point in time of about 57.4 (sec).

As can be seen from the rolling motor current graph 600, when the hotband 13 of the steel sheet 10 reaches the rolling roll 351, the currentof the rolling motor 354 increases and reaches an upper limit. As can beseen from the rolling roll speed graph 601, after the hot band 13 of thesteel sheet 10 reaches the rolling roll 351, the rolling roll speedbecomes 0 (zero) and the conveyance of the steel sheet 10 is stopped inthe rolling mill 350.

It is considered that this is partly because the rolling speed controldevice 570 and the rolling gap control device 580 operate as follows.When the hot band 13 reaches the rolling roll 351, force in a directionof increasing the rolling roll gap is added to the rolling roll 351. Inthis case, the rolling control unit of the rolling gap control device580 controls the upper rolling roll 351 to reduce the steel sheet 10with strong force by the rolling mill power cylinder 353 in order to setthe rolling roll gap to the first rolling roll gap. The speed controlunit of the rolling speed control device 570 controls to maintain therolling roll speed. However, since the upper rolling roll 351 reducesthe steel sheet 10 with a strong force, the speed control unit of therolling speed control device 570 increases the current of the rollingmotor 354 to increase the torque of the rolling motor 354 in order tomaintain the rolling roll speed. In this manner, the current of therolling motor 354 reaches the upper limit. Finally, the torque of therolling motor 354 cannot be increased and the rolling roll 351 cannotwithstand the force of reducing the steel sheet 10. Therefore, and therolling roll speed becomes 0 (zero).

As shown in the rolling motor current graph 600, when the hot band 13 ofthe steel sheet 10 reaches the rolling roll 351, the current of therolling motor 354 increases and reaches the upper limit. From the above,in a case where the current of the rolling motor 354 continuouslyexceeds a current threshold value I1 during a hot band determinationtime T1, it can be determined that the hot band 13 reaches the rollingmotor 354. The current threshold value I1 is a threshold value of acurrent used for the determination for the hot band 13. The currentthreshold value I1 is a current that does not flow through the rollingmotor 354 during normal rolling and is a current flowing through therolling motor 354 after the hot band 13 reaches the rolling roll 351.The current threshold value I1 is set in advance based on the rollingmotor current graph 600. The hot band determination time T1 is set inadvance in order to prevent erroneous determination.

Roll Opening

Next, a necessity of the roll opening at the time of hot band occurrencewill be described with reference to the rolling roll speed graph 601 ofFIG. 6 . As described above, when the hot band 13 of the steel sheet 10reaches the rolling roll 351 and then the rolling control unit of therolling gap control device 580 continues the rolling control, therolling roll speed becomes 0 (zero) and the conveyance of the steelsheet 10 is stopped in the rolling mill 350. In a case where the hotband 13 reaches the rolling roll 351, the roll opening is performed andit waits for the hot band 13 to pass through the rolling roll 351.Accordingly, it is possible to avoid the rolling roll speed frombecoming 0 (zero).

Amount of Wedge

Next, an amount of wedge of the steel sheet 10 will be described withreference to FIG. 7 . FIG. 7 is a cross-sectional view of an example ofthe steel sheet 10.

The amount of wedge of the steel sheet 10 is a difference in thethickness of both end portions of the steel sheet 10. The amount ofwedge of the steel sheet 10 is defined by the following equation (1).Amount of wedge=|ta−tb|  (1)

Here, ta is a thickness of the steel sheet 10 at a position w (mm) fromone end portion in the width direction of the steel sheet 10. tb is athickness of the steel sheet 10 at a position w (mm) from the other endportion in the width direction of the steel sheet 10. For example, 25(mm) is used as w (mm).

In the twin roll-type continuous casting machine 150, the molten steelis changed to a sheet-shaped steel sheet 10 by the pair of casting rolls201. In the twin roll-type continuous casting machine 150, the amount ofwedge tends to be large since there are many unstable operating elementssuch as easy occurrence of the hot band, compared with the normalcontinuous casting machine.

When the steel sheet 10 having a large amount of wedge passes throughthe rolling roll 351, a rolling reduction difference occurs between oneend portion and the other end portion in the width direction of thesteel sheet 10 having the large amount of wedge according to the sheetthickness control and a speed difference occurs between one end portionand the other end portion in the width direction. This speed differencecauses the meandering. Therefore, in a case where the twin roll-typecontinuous casting machine 150, which tends to have a large amount ofwedge, is used, the speed difference tends to be large and themeandering tends to be larger than in a case where the normal continuouscasting machine is used. When the steel sheet 10 meanders, the steelsheet 10 contacts an instrument or the like, which causes the instrumentor the like to break down or the steel sheet 10 to defect.

In a case where the meandering of the steel sheet 10 occurs, the rollopening is performed and it waits for a portion of the steel sheet 10having the large amount of wedge to pass through the rolling roll 351.Therefore, it is possible to avoid the instrument or the like frombreaking down due to the meandering of the steel sheet 10.

Tension Control at Time of Roll Opening

Next, an operation of a casting and rolling system as a comparativeexample in a case where the roll opening is performed when the tensioncontrol is performed will be described with reference to FIGS. 8A to 8D.FIG. 8A is a diagram showing a casting roll speed graph representing atime change of the casting roll speed. FIG. 8B is a diagram showing afirst pinch roll speed graph representing a time change of the firstpinch roll speed. FIG. 8C is a diagram showing a second pinch roll speedgraph representing a time change of the second pinch roll speed. FIG. 8Dis a diagram showing a rolling roll speed graph representing the timechange of the rolling roll speed. The casting and rolling system as thecomparative example has the same configuration as the casting androlling system 1 according to the present embodiment. However, unlike anoperation of the casting and rolling system 1 according to the presentembodiment which will be described below with reference to FIG. 9 , theconveyor control device 550 only performs the tension control in thecasting and rolling system as the comparative example.

Data of FIGS. 8A to 8D are obtained when the casting and the rolling areactually performed using the casting and rolling system as thecomparative example. In the casting and rolling system as thecomparative example, the tension control unit 560 of the first conveyorcontrol device 550A and the tension control unit 560 of the secondconveyor control device 550B perform the tension control. In the castingand rolling system as the comparative example, the rolling control unitof the rolling gap control device 580 performs the rolling control.However, at a point in time of about 91 (sec), the rolling control unitof the rolling gap control device 580 stops the rolling control and theopen control unit of the rolling gap control device 580 starts the opencontrol to perform the roll opening. Even after the roll opening isperformed, the tension control unit 560 continues the tension control.

As will be described below, at a point in time of about 93 (sec), theoperation of the casting and rolling system 1 is stopped in the castingand rolling system as the comparative example.

As shown in FIGS. 8A to 8D, the casting roll speed, the first pinch rollspeed, the second pinch roll speed, and the rolling roll speed aresubstantially the same speed until the roll opening is performed.Therefore, it can be said that a sheet slip of the steel sheet 10 doesnot occur. The sheet slip of the steel sheet 10 is a state where thesteel sheet 10 is slipped on the roll such as the pinch roll 301.

The casting roll speed and the rolling roll speed are maintained atpositive values even when the roll opening is performed, as shown fromthe point in time of about 91 (sec) to the point in time of about 93(sec) in FIGS. 8A and 8D. In FIGS. 8A to 8D, the roll opening isperformed at the point in time of about 91 (sec). On the other hand, thefirst pinch roll speed and the second pinch roll speed suddenly changeto negative values when the roll opening is performed, as shown near thepoint in time of about 91 (sec) in FIGS. 8B and 8C. The fact that thefirst pinch roll speed and the second pinch roll speed are the negativevalues represents that the first pinch roll 301A and the second pinchroll 301B rotate in a reverse direction to convey the steel sheet 10 ina direction opposite to the direction of the rolling mill 350. Here, itis considered that the steel sheet 10 is conveyed at a speed close tothe casting roll speed in the casting and rolling equipment 100 and isalways conveyed in the direction of the rolling mill 350 when viewedfrom the pinch roll 301 in a time zone before and after the rollopening. At a moment when the first pinch roll 301A and the second pinchroll 301B rotate in the reverse direction at the point in time of about91 (sec) when the roll opening is performed, the steel sheet 10 is notsuddenly conveyed in the opposite direction along with the reverserotation. Therefore, it can be said that the sheet slip of the steelsheet 10 occurs in the first pinch roll 301A and the second pinch roll301B.

It is considered that the following operation causes the sheet slip ofthe steel sheet 10 to occur due to the roll opening. That is, thetension of the steel sheet 10 fluctuates greatly due to the rollopening. At this time, the tension control unit 560 continues thetension control even after the roll opening. Therefore, the tensioncontrol unit 560 of the first conveyor control device 550A greatlychanges the torque of the first conveyance motor 303A in order tomaintain the tension of the steel sheet 10 to the first tension.Accordingly, a rotation speed of the first conveyance motor 303Afluctuates greatly. As a result, the sheet slip of the steel sheet 10occurs in the first pinch roll 301A. Similarly, the sheet slip of thesteel sheet 10 occurs also in the second pinch roll 301B.

As can be seen from the first pinch roll speed graph of FIG. 8B, whenthe sheet slip of the steel sheet 10 occurs due to the roll opening, thesheet slip of the steel sheet 10 continues and the sheet slip of thesteel sheet 10 is not eliminated in the first pinch roll 301A.Therefore, as shown in FIGS. 8A to 8D, the casting roll speed, the firstpinch roll speed, the second pinch roll speed, and the rolling rollspeed are all 0 (zero) at the latest at a point in time of time 95 (sec)to stop the operation of the casting and rolling system 1.

When the sheet slip of the steel sheet 10 occurs, it is impossible toperform the tension control and to normally roll the steel sheet 10. Theroll may defect due to the sheet slip of the steel sheet 10. Therefore,even in a case where the sheet slip of the steel sheet 10 occurs whenthe roll opening is performed, it is necessary to eliminate the sheetslip of the steel sheet 10 in a short time.

Control Processing

Next, control processing according to the present embodiment will bedescribed with reference to FIG. 9 . FIG. 9 is a flowchart showing anexample of the control processing. With the control processing accordingto this embodiment, it is possible to eliminate the sheet slip of thesteel sheet 10 in a short time. The control processing of FIG. 9 isexecuted by the main control device 500.

In S100, the processing management unit 517 refers to the storage device502 or receives information from an external device by networkcommunication to acquire various parameters of the casting and rollingequipment 100. The processing management unit 517 performs an initialsetting such that the casting and rolling equipment 100 performs anoperation corresponding to the acquired various parameters. The variousparameters acquired by the processing management unit 517 include thefirst tension, the first tension range, the first tension determinationtime, the second tension, the second tension range, the second tensiondetermination time, the first speed, the first speed range, the firstspeed determination time, the second speed, the second speed range, thesecond speed determination time, the first rolling roll gap, the secondrolling roll gap, and the like.

The first control unit 510 controls the casting and rolling equipment100 to perform the casting and the rolling. At this time, the firstcontrol unit 510 transmits a command to the rolling gap control device580 through the communication interface 503 to control the rollingcontrol unit of the rolling gap control device 580 to perform therolling control. The first control unit 510 transmits a command to thefirst conveyor control device 550A and the second conveyor controldevice 550B through the communication interface 503 to control thetension control unit 560 of the first conveyor control device 550A toperform the tension control and to control the tension control unit 560of the second conveyor control device 550B to perform the tensioncontrol. The first control unit 510 transmits a command to the rollingspeed control device 570 through the communication interface 503 tocontrol the speed control unit of the rolling speed control device 570to perform the speed control.

In S101, the processing management unit 517 controls to start processingof S102, S103, and S104 in parallel.

In S102, the abnormality determination unit 514 determines whether ornot the steel sheet 10 meanders based on the amount of meanderingacquires from the meandering meter 254. The abnormality determinationunit 514 determines that the steel sheet 10 meanders in a case where theamount of meandering continuously exceeds a meandering amount rangeduring a meandering determination time. The meandering amount range isdetermined in advance by an experiment or the like as a range thatsatisfies a condition such as non-contact of the steel sheet 10 with theinstrument or the like. The meandering determination time is forpreventing erroneous detection of the meandering of the steel sheet 10and is determined in advance by an experiment, a simulation, or thelike. The abnormality determination unit 514 advances the processing toS105 in a case where determination is made that the steel sheet 10meanders, and executes S102 again in a case where determination is madethat the steel sheet 10 does not meander.

In S103, the abnormality determination unit 514 determines whether ornot the hot band 13 occurs based on the current flowing through therolling motor 354. As already described above, the abnormalitydetermination unit 514 determines that the hot band 13 occurs in thecase where the current of the rolling motor 354 continuously exceeds thecurrent threshold value 11 during the hot band determination time T1.The abnormality determination unit 514 may acquire the current flowingthrough the rolling motor 354 from the rolling speed control device 570or may acquire the current from an ammeter that measures the current ofthe rolling motor 354. The abnormality determination unit 514 advancesthe processing to S105 in a case where determination is made that thehot band 13 occurs, and executes S103 again in a case wheredetermination is made that the hot band 13 does not occur.

In S104, the abnormality determination unit 514 determines whether ornot the operator performs an opening instruction based on an operationof the operator received by the input device 504 included in the maincontrol device 500, the information received from the external device,or the like. The abnormality determination unit 514 advances theprocessing to S105 in a case where determination is made that theoperator performs the opening instruction and executes S104 again in acase where determination is made that the operator does not perform theopening instruction.

In S105, the abnormality determination unit 514 advances the processingto S106 in a case where the processing advances to S105 from S102, S103,or S104 or any combination thereof. The processing management unit 517controls to stop the processing of S102, S103, and S104 in execution ina case where the processing advances to S105 and in a case where theprocessing of S102, S103, or S104 or any combination thereof isexecuted.

In S106, the processing management unit 517 controls to start processingof S107, S108, and S109 in parallel.

In S107, the second control unit 511 controls to change a control methodof the first pinch roll 301A from the tension control to the speedcontrol. More specifically, the second control unit 511 transmits acommand to the first conveyor control device 550A through thecommunication interface 503 to control the speed control unit 561 of thefirst conveyor control device 550A to start the speed control.Thereafter, the second control unit 511 advances the processing to S110.

In S108, the second control unit 511 controls to change a control methodof the second pinch roll 301B from the tension control to the speedcontrol. More specifically, the second control unit 511 transmits acommand to the second conveyor control device 550B through thecommunication interface 503 to control the speed control unit 561 of thesecond conveyor control device 550B to start the speed control.Thereafter, the second control unit 511 advances the processing to S110.

In S109, the second control unit 511 controls to perform the rollopening. More specifically, the second control unit 511 transmits acommand to the rolling gap control device 580 through the communicationinterface 503 to control the open control unit of the rolling gapcontrol device 580 to start the open control. Accordingly, the rollopening is performed. Thereafter, the second control unit 511 advancesthe processing to S110.

In S110, the processing management unit 517 advances the processing toS111 after the processing of S107, S108, and S109 ends.

In S111, the processing management unit 517 controls to start processingof S112, S113, and S114 in parallel.

In S112, the speed determination unit 515 determines whether or not afirst standby time elapses since the processing of S107 is performed.The first standby time is a time from when the roll opening is performedand the speed control is started until the first pinch roll speed andthe second pinch roll speed are stabilized by the speed control and isset by performing an experiment or a simulation in advance. The firststandby time is indicated as TFr in FIGS. 10B and 10C described below.The speed determination unit 515 advances the processing to S115 in acase where the processing of S107 is performed and then determination ismade that the first standby time elapses, and executes S112 again in acase where determination is made that the first standby time does notelapse.

In S113, the speed determination unit 515 determines whether or not thefirst pinch roll speed is stabilized at the first speed. As alreadydescribed above, the speed determination unit 515 determines that thefirst pinch roll speed is stabilized at the first speed in a case wherethe first pinch roll speed continuously falls in the first speed rangeduring the first speed determination time. The speed determination unit515 acquires the first pinch roll speed from, for example, the firstconveyor control device 550A. The speed determination unit 515 advancesthe processing to S115 in a case where determination is made that thefirst pinch roll speed is stabilized at the first speed, and executesS113 again in a case where determination is made that the first pinchroll speed is not stabilized at the first speed. The first speed, thefirst speed range, and the first speed determination time arerespectively indicated as V1, R1, and TV1 in FIG. 10B, which will bedescribed below.

In S114, the speed determination unit 515 determines whether or not thesecond pinch roll speed is stabilized at the second speed. As alreadydescribed above, the speed determination unit 515 determines that thesecond pinch roll speed is stabilized at the second speed in a casewhere the second pinch roll speed continuously falls in the second speedrange during the second speed determination time. The speeddetermination unit 515 acquires the second pinch roll speed from, forexample, the second conveyor control device 550B. The speeddetermination unit 515 advances the processing to S115 in a case wheredetermination is made that the second pinch roll speed is stabilized atthe second speed, and executes S114 again in a case where determinationis made that the second pinch roll speed is not stabilized at the secondspeed. The second speed, the second speed range, and the second speeddetermination time are respectively indicated as V2, R2, and TV2 in FIG.10C, which will be described below.

In the above S112, S113, and S114, the speed determination unit 515performs processing of waiting until the first pinch roll speed and thesecond pinch roll speed are stabilized by the speed control.

In S115, the processing management unit 517 advances the processing toS116 after the processing of S112, S113, and S114 end.

In S116, the third control unit 512 transmits a command to the rollinggap control device 580 through the communication interface 503 tocontrol the light reduction control unit of the rolling gap controldevice 580 to start the light reduction control. Accordingly, therolling miii 350 starts the processing of lightly reducing the steelsheet 10. It is considered that an abnormal portion of the steel sheet10 such as the hot band 13 of the steel sheet 10 or the portion of thesteel sheet 10 having the large amount of wedge, which causes themeandering of the steel sheet 10, passes through the rolling roll 351during a period from when the roll opening is performed in S109 untilthe light reduction is started in S116. In a case where the abnormalportion of the steel sheet 10 remains during the period from when theroll opening is performed in S109 until the light reduction is startedin S116, S109 and subsequent processing are executed again afterprocessing of S126 or S127, and S116 is executed after the roll openingis performed and the pinch roll speed is stabilized. Therefore, finallyall the abnormal portions of the steel sheet 10 pass through the rollingroll 351.

In S117, the processing management unit 517 controls to start theprocessing of S118 and S119 in parallel.

In S118, the third control unit 512 controls to change the controlmethod of the first pinch roll 301A from the speed control to thetension control. More specifically, the third control unit 512 transmitsa command to the first conveyor control device 550A through thecommunication interface 503 to control the tension control unit 560 ofthe first conveyor control device 550A to start the tension control.Thereafter, the third control unit 512 advances the processing to S120.

In S119, the third control unit 512 controls to change the controlmethod of the second pinch roll 301B from the speed control to thetension control. More specifically, the third control unit 512 transmitsa command to the second conveyor control device 550B through thecommunication interface 503 to control the tension control unit 560 ofthe second conveyor control device 550B to start the tension control.Thereafter, the third control unit 512 advances the processing to S120.

In S120, the processing management unit 517 advances the processing toS121 after the processing of S118 and S119 ends.

In S121, the processing management unit 517 controls to start processingof S122, S123, and S124 in parallel.

In S122, the tension determination unit 516 determines whether or not asecond standby time elapses since the processing of S118 is performed.The second standby time is a time from the tension control is starteduntil the rear surface tension of the first pinch roll 301A and the rearsurface tension of the second pinch roll 301B are stabilized and is setby performing an experiment or a simulation in advance. The tensiondetermination unit 516 advances the processing to S125 in a case wherethe processing of S118 is performed and then determination is made thatthe second standby time elapses, and executes S122 again in a case wheredetermination is made that the second standby time does not elapse.

In S123, the tension determination unit 516 determines whether or notthe rear surface tension of the first pinch roll 301A is stabilized atthe first tension. As already described above, the tension determinationunit 516 determines that the rear surface tension of the first pinchroll 301A is stabilized at the first tension in a case where the rearsurface tension of the first pinch roll 301A is continuously in thefirst tension range during the first tension determination time. Thetension determination unit 516 calculates and uses the rear surfacetension of the first pinch roll 301A based on, for example, an output ofan ammeter that measures the current of the first conveyance motor 303A.The tension determination unit 516 advances the processing to S125 in acase where determination is made that the rear surface tension of thefirst pinch roll 301A is stabilized at the first tension, and executesS123 again in a case where determination is made that the rear surfacetension of the first pinch roll 301A is not stabilized at the firsttension.

In S124, the tension determination unit 516 determines whether or notthe rear surface tension of the second pinch roll 301B is stabilized atthe second tension. As already described above, the tensiondetermination unit 516 determines that the rear surface tension of thesecond pinch roll 301B is stabilized at the second tension in a casewhere the rear surface tension of the second pinch roll 301B iscontinuously in the second tension range during the second tensiondetermination time. The tension determination unit 516 calculates anduses the rear surface tension of the second pinch roll 301B based on,for example, an output of an ammeter that measures the current of thesecond conveyance motor 303B. The tension determination unit 516advances the processing to S125 in a case where determination is madethat the rear surface tension of the second pinch roll 301B isstabilized at the second tension, and executes S124 again in a casewhere determination is made that the rear surface tension of the secondpinch roll 301B is not stabilized at the second tension.

In S122, S123, and S124 described above, the tension determination unit516 performs processing of waiting until the tension of the steel sheet10 is stabilized by the tension control.

In S125, the processing management unit 517 advances the processing toS126 after the processing of S122, S123, and S124 ends.

In S126, the abnormality determination unit 514 determines whether ornot the steel sheet 10 meanders based on the amount of meanderingacquired from the meandering meter 254 in the same manner as in S102.The abnormality determination unit 514 returns the processing to S106 ina case where determination is made that the steel sheet 10 meanders, andadvances the processing to S127 in a case where determination is madethat the steel sheet 10 does not meander.

In S127, the abnormality determination unit 514 determines whether ornot the hot band 13 occurs based on the current flowing through therolling motor 354 in the same manner as in S103. The abnormalitydetermination unit 514 returns the processing to S106 in a case wheredetermination is made that the hot band 13 occurs, and advances theprocessing to S128 in a case where determination is made that the hotband 13 does not occur.

In S128, the third control unit 512 transmits a command to the rollinggap control device 580 through the communication interface 503 tocontrol the rolling control unit of the rolling gap control device 580to resume the rolling control. Accordingly, the rolling mill 350 resumesthe processing of rolling the steel sheet 10. Thereafter, the processingmanagement unit 517 ends the processing of FIG. 9 .

Operation Example

Next, an operation example of the control processing of FIG. 9 will bedescribed with reference to FIGS. 10A to 10D. FIG. 10A is a diagramshowing the casting roll speed graph representing the time change of thecasting roll speed. FIG. 10B is a diagram showing the first pinch rollspeed graph representing the time change of the first pinch roll speed.FIG. 10C is a diagram showing the second pinch roll speed graphrepresenting the time change of the second pinch roll speed. FIG. 10D isa diagram showing the rolling roll speed graph representing the timechange of the rolling roll speed.

The V1, R1, and TV1 in FIG. 10B are respectively the first speed, thefirst speed range, and the first speed determination time alreadydescribed. The V2, R2, and TV2 in FIG. 10C are respectively the secondspeed, the second speed range, and the second speed determination timealready described. The TFr in FIGS. 10B and 10C is the first standbytime already described.

In the operation example shown in FIGS. 10A to 10D, the operatorperforms the opening instruction, and the roll opening is performed bythe processing of S109 in FIG. 9 at a point in time of about 148.6(sec). At this time, a control method of the pinch roll 301 is changedfrom the tension control to the speed control in S107 and S108 in FIG. 9, as shown in the first pinch roll speed graph of FIG. 10B and thesecond pinch roll speed graph 622 of FIG. 10C.

Thereafter, in a case where determination is made that the pinch rollspeed is stabilized by the speed control in the processing of S112,S113, and S114, the control method of the pinch roll 301 is changed fromthe speed control to the tension control in S118 and S119.

The casting roll speed and the rolling roll speed are maintained atpositive values before and after the roll opening, as shown near thepoint in time of about 148.5 (sec) when the roll opening is performed inFIGS. 10A and 10D. On the other hand, the first pinch roll speed and thesecond pinch roll speed suddenly change before and after the rollopening is performed and change from positive values to negative values,as shown near the point in time of about 148.5 (sec) when the rollopening is performed in FIGS. 10B and 10C. Therefore, it can be saidthat the sheet slip of the steel sheet 10 occurs in the first pinch roll301A and the second pinch roll 301B immediately after the roll openingis performed, as in the operation example described with reference toFIGS. 8A to 8D.

However, with the start of the speed control at the time of the rollopening, the first pinch roll speed and the second pinch roll speedbecome the same speeds as the casting roll speed and the rolling rollspeed within 0.5 (sec) after the roll opening. Therefore, it can be saidthat the sheet slip of the steel sheet 10 is eliminated within 0.5 (sec)after the roll opening.

Thereafter, even after the tension control is started, the first pinchroll speed and the second pinch roll speed are maintained at the samespeeds as the casting roll speed and the rolling roll speed. Therefore,normal rolling is possible.

As described above, the sheet slip of the steel sheet 10 is eliminatedin a short time by the control processing of FIG. 9 , even in a casewhere the roll opening is performed. It is possible to resume the normalrolling even after the roll opening is performed in the casting androlling system 1 according to the present embodiment, unlike theoperation of the casting and rolling system as the comparative exampledescribed with reference to FIGS. 8A to 8D.

Effect

When the rolling is continued in a case where the abnormality occurs inthe steel sheet 10, the rolling roll speed becomes 0 (zero) which causesthe rolling to stop, or the steel sheet 10 contacts the instrument orthe like due to the meandering of the steel sheet 10 which causes theinstrument or the like to break down, as already described above. Whenthe end portion of the steel sheet 10 in the width direction contactsthe instrument or the like due to the meandering of the steel sheet 10,the steel sheet 10 may be bent which causes the rolling not to becontinued. Therefore, unsteady work such as work for resuming therolling or work for repairing the instrument or the like is required.For this reason, it is impossible to continue the rolling of the steelsheet 10 stably.

On the other hand, in the present embodiment, the roll opening isperformed by the open control in a case where the abnormality occurs inthe steel sheet 10. Therefore, it is possible to avoid the rolling fromstopping or the instrument or the like from breaking down, and it ispossible to continue the rolling of the steel sheet 10 stably.

When the tension control is continued in a case where the roll openingis performed, the sheet slip of the steel sheet 10 occurs in the pinchroll 301 as already described above. The sheet slip continues withoutbeing eliminated. Therefore, the pinch roll 301 defects, and unsteadywork such as replacement of the pinch roll 301 is required. As a result,it is necessary to stop the rolling. Therefore, it is impossible tocontinue the rolling of the steel sheet 10 stably. When the sheet slipof the steel sheet 10 continues, it is impossible to perform the tensioncontrol and thus roll the steel sheet 10 normally.

On the other hand, in the present embodiment, the control method of thepinch roll 301 is changed from the tension control to the speed controlafter the roll opening. Therefore, it is possible to eliminate the sheetslip of the steel sheet 10 and thus suppress the occurrence of unsteadywork such as replacement of the pinch roll 301, as already describedabove. Therefore, it is possible to continue the rolling of the steelsheet 10 stably.

In the present embodiment, the third control unit 512 controls therolling gap control device 580 to resume the rolling control after theconveyor control device 550 resumes the tension control. Therefore, therolling is automatically resumed. Therefore, it is possible to continuethe rolling of the steel sheet 10 stably.

The twin roll-type continuous casting machine 150 discharges the steelsheet 10 to the conveyor 300. Here, when the rolling is continued in acase where the abnormality occurs in the steel sheet 10, the rolling isstopped as described above. For this reason, it is impossible to conveythe steel sheet 10 and it is necessary to stop the twin roll-typecontinuous casting machine 150. In a case where the twin roll-typecontinuous casting machine 150 is used, the manufacturing of the steelsheet is continuously performed from the twin roll-type continuouscasting machine 150 to the winding of the steel sheet 10 after hotrolling, and the molten steel is in between the pair of casting rolls201 and is rapidly cooled. Therefore, the molten steel between the pairof casting rolls 201 has a high solid proportion in a solid-liquidcoexistence state. When the twin roll-type continuous casting machine150 is stopped in this state, the molten steel solidifies in the pouringbasin 210 or between the pair of casting rolls 201. It is necessary toclean the pouring basin 210 and to check and clean a sticking state ofthe steel between the pair of casting rolls 201 in order to remove thesolidified molten steel, and it takes a lot of time for such unsteadywork. However, in the present embodiment, even in a case where theabnormality occurs in the steel sheet 10, the conveyance of the steelsheet 10 is not stopped. Therefore, the unsteady work to remove thesolidified molten steel is unnecessary. Therefore, it is possible tocontinue the rolling of the steel sheet 10 stably.

The third control unit 512 controls the rolling gap control device 580to perform the light reduction control and then controls to resume thetension control. Therefore, when the tension control is resumed, therolling roll 351 lightly reduces the steel sheet 10. Therefore, it ispossible to apply the tension to the steel sheet 10 between the pinchroll 301 and the rolling roll 351 by the tension control.

In a case where it is determined that there is the abnormality in thesteel sheet 10 after the tension control is resumed by the control bythe third control unit 512, the second control unit 511 controls therolling gap control device 580 to perform the open control and controlsthe conveyor control device 550 to perform the speed control. Therefore,the rolling control is not resumed until the abnormality in the steelsheet 10 is eliminated. Therefore, when the rolling control is resumed,it is possible to reliably perform the normal rolling.

The abnormality determination unit 514 determines that there is theabnormality in the steel sheet 10 in the case where determination ismade that the steel sheet 10 meanders or the case where determination ismade that there is the abnormal sheet thickness fluctuation in the steelsheet 10 or a combination thereof. Therefore, it is possible to reliablydetect the usually assumed abnormality in the steel sheet 10 in thecasting and rolling system 1.

The abnormality determination unit 514 determines whether or not the hotband 13 occurs in the steel sheet 10 based on the current of the rollingmotor 354. Therefore, it is possible to perform simple processing fordetermining the occurrence of the hot band 13.

The speed determination unit 515 determines that the first pinch rollspeed is stabilized at the first speed in a case where the first pinchroll speed is continuously in the first speed range during the firstspeed determination time. The speed determination unit 515 determinesthat the second pinch roll speed is stabilized at the second speed in acase where the second pinch roll speed is continuously in the secondspeed range during the second speed determination time. Therefore, it ispossible to prevent erroneous detection that the pinch roll speed isstabilized.

Modification Example

In the above embodiment, the tension determination unit 516 controls therear surface tension of the conveyor 300. However, the tensiondetermination unit 516 may be configured to control front tension of theconveyor 300. The front tension is tension of the steel sheet 10 on afront side (side opposite to the advancing direction of the steel sheet10) of the conveyor 300.

The casting and rolling equipment 100 includes two conveyors 300, butthe conveyor 300 may be one or three or more.

In the above embodiment, the main control device 500 includes the inputdevice 504. However, the conveyor control device 550 may include aninput device that receives an input from the operator. The conveyorcontrol device 550 transmits information indicating that the openinginstruction is received to the main control device 500 in a case wherethe opening instruction by the operator is received through the inputdevice. In S104 in FIG. 9 , the abnormality determination unit 514 ofthe main control device 500 determines that the operator performs theopening instruction based on the information received from the conveyorcontrol device 550. The rolling speed control device 570 or the rollinggap control device 580 or a combination thereof may include an inputdevice that receives an input from the operator.

Although the present invention has been described above together withthe embodiments, the above embodiments are merely examples of embodimentof the present invention, and the technical scope of the presentinvention should not be interpreted in a limited manner by theembodiments. That is, the present invention can be implemented invarious forms without departing from the technical idea or the mainfeatures thereof.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to continue therolling stably.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

1: casting and rolling system

100: casting and rolling equipment

101: control system

150: twin roll-type continuous casting machine

300: conveyor

350: rolling mill

400: looper

450: coiler

500: main control device

550: conveyor control device

570: rolling speed control device

580: rolling gap control device

The invention claimed is:
 1. A control system of casting and rollingequipment including a twin roll-type continuous casting machine, arolling mill that rolls a steel sheet with a pair of rolling rolls, anda conveyor that conveys the steel sheet in a direction of the rollingmill with a pair of conveyance rolls, in which the twin roll-typecontinuous casting machine includes a pair of casting rolls that rotatesin directions opposite to each other, the pair of the casting rollscools molten steel injected into an upper pouring basin between the pairof the casting rolls and pressure-contacts the cooled and solidifiedmolten steel to discharge the steel sheet from between the pair of thecasting rolls, and the conveyor conveys the steel sheet discharged fromthe twin roll-type continuous casting machine in the direction of therolling mill, the control system comprising: a rolling mill control unitconfigured to control the rolling mill by any one of controls includinga rolling control of rolling the steel sheet with a set roll gap and anopen control that performs a control such that at least one of the pairof the rolling rolls does not contact the steel sheet; a conveyorcontrol unit configured to control the conveyor by any one of controlsincluding a tension control that conveys the steel sheet at set tensionof the steel sheet and a speed control that conveys the steel sheet at aset rotation speed of the conveyance rolls; a first control unitconfigured to control the rolling mill control unit to perform therolling control and controls the conveyor control unit to perform thetension control; a second control unit configured to control the rollingmill control unit to perform the open control and controls the conveyorcontrol unit to perform the speed control in a case where determinationis made that there is an abnormality in the steel sheet while therolling control and the tension control started by the control by thefirst control unit are performed; and a third control unit configured tocontrol the conveyor control unit to resume the tension control andcontrols the rolling mill control unit to resume the rolling control ina case where determination is made that the conveyance rolls arestabilized at the set rotation speed by the speed control started by thecontrol by the second control unit.
 2. The control system according toclaim 1, wherein the rolling mill control unit controls the rolling millby any one of controls including the rolling control, the open control,and a light reduction control that lightly reduces the steel sheet witha roll gap larger than the set roll gap, and the third control unitcontrols the rolling mill control unit to perform the light reductioncontrol, then controls the conveyor control unit to resume the tensioncontrol, and then controls the rolling mill control unit to resume therolling control, in a case where determination is made that the pair ofconveyance rolls is stabilized at the set rotation speed by the speedcontrol started by the control by the second control unit.
 3. Thecontrol system according to claim 2, wherein the third control unitcontrols the rolling mill control unit to perform the light reductioncontrol, then controls the conveyor control unit to resume the tensioncontrol, and then controls the rolling mill control unit to resume therolling control in a case where determination is made that there is noabnormality in the steel sheet, in a case where determination is madethat the pair of conveyance rolls are stabilized at the set rotationspeed by the speed control started by the control by the second controlunit, and the second control unit controls the rolling mill control unitto perform the open control and controls the conveyor control unit toperform the speed control, in a case where determination is made thatthere is an abnormality in the steel sheet after the tension control isresumed by the control by the third control unit or in a case wheredetermination is made that there is an abnormality in the steel sheetwhile the rolling control and the tension control started by the controlby the first control unit are performed.
 4. The control system accordingto claim 1, further comprising: an abnormality determination unit thatdetermines that there is the abnormality in the steel sheet in a casewhere determination is made that the steel sheet meanders or a casewhere determination is made that there is an abnormal sheet thicknessfluctuation in the steel sheet or a combination thereof, wherein thesecond control unit controls the rolling mill control unit to performthe open control and controls the conveyor control unit to perform thespeed control, in a case where the abnormality determination unitdetermines that there is an abnormality in the steel sheet while therolling control and the tension control started by the control by thefirst control unit are performed.
 5. The control system according toclaim 4, wherein the abnormality determination unit determines whetheror not the abnormal sheet thickness fluctuation occurs in the steelsheet based on a current of a motor that rotates the rolling roll. 6.The control system according to claim 1, further comprising: a speeddetermination unit that determines that the conveyance rolls arestabilized at the set rotation speed in a case where the rotation speedof the conveyance rolls continuously falls in a set range for a settime, wherein the third control unit controls the conveyor control unitto resume the tension control and controls the rolling mill control unitto resume the rolling control, in a case where the speed determinationunit determines that the conveyance rolls are stabilized at the setrotation speed after the speed control is started by the control by thesecond control unit.
 7. A control device that controls casting androlling equipment including a twin roll-type continuous casting machine,a rolling mill that rolls a steel sheet with a pair of rolling rolls, aconveyor that conveys the steel sheet in a direction of the rolling millwith a pair of conveyance rolls, a rolling mill control unit configuredto control the rolling mill by any one of controls including a rollingcontrol of rolling the steel sheet with a set roll gap and an opencontrol that performs a control such that at least one of the pair ofthe rolling rolls does not contact the steel sheet, a conveyor controlunit configured to control the conveyor by any one of controls includinga tension control that conveys the steel sheet at set tension of thesteel sheet and a speed control that conveys the steel sheet at a setrotation speed of the conveyance rolls, in which the twin roll-typecontinuous casting machine includes a pair of casting rolls that rotatesin directions opposite to each other, the pair of the casting rollscools molten steel injected into an upper pouring basin between the pairof the casting rolls and pressure-contacts the cooled and solidifiedmolten steel to discharge the steel sheet from between the pair of thecasting rolls, and the conveyor conveys the steel sheet discharged fromthe twin roll-type continuous casting machine in the direction of therolling mill, the control device comprising: a first control unitconfigured to control the rolling mill control unit to perform therolling control and controls the conveyor control unit to perform thetension control; a second control unit configured to control the rollingmill control unit to perform the open control and controls the conveyorcontrol unit to perform the speed control in a case where determinationis made that there is an abnormality in the steel sheet while therolling control and the tension control started by the control by thefirst control unit are performed; and a third control unit configured tocontrol the conveyor control unit to resume the tension control andcontrols the rolling mill control unit to resume the rolling control ina case where determination is made that the conveyance rolls arestabilized at the set rotation speed by the speed control started by thecontrol by the second control unit.